1. Field of the Invention
The invention relates to electric power steering systems.
2. Description of the Related Art
Conventionally, electric power steering systems (EPSs) are known in the art which assist driver's steering operation by applying power of a motor to a steering mechanism of a vehicle. In such EPSs, if the driver operates a steering wheel so that a rack end continuously hits a housing or the motor is continuously driven with high power, the motor may be continuously subjected to high load, which may cause overheating of the motor etc. For example, in an EPS of Japanese Patent Application Publication No. 2010-126081 (JP 2010-126081 A), a current command value for the motor is limited in order to prevent overheating.
When the current command value is being limited in the EPS of JP 2010-126081 A, appropriate assist control cannot be performed even when the driver turns back a steering wheel. The driver therefore feels unsmoothness in steering operation. The driver has this feeling of unsmoothness as an actual assist force becomes different from a target assist force due to the limitation of the current command value. That is, since the actual assist force does not quickly follow target assist force, the driver feels a rapid change in steering feeling.